1. Field of the Invention
The present invention relates to a vapor-phase deposition apparatus and a vapor-phase deposition method, either designed for use in manufacture of semiconductor devices or the like.
2. Description of the Related Art
Various vapor-phase deposition apparatuses are known which performs vapor-phase deposition to form semiconductor films or the like on a crystal substrate, thereby to manufacture semiconductor devices or the like. A typical vapor-phase deposition apparatus comprises a base plate, a reaction vessel secured to the base plate in airtight fashion, a shaft passing through the base plate into the vessel, a substrate holder located within the vessel and rotatably supported by the shaft, for holding a crystal substrate, and a heater located within the vessel, for heating the holder and a crystal substrate held by the holder.
The reaction vessel has a gas-inlet port in the top, and a gas-outlet port in the bottom. Gases (e.g., feed gas, carrier gas, etc.) are supplied into the vessel through the gas-inlet port. Any gas that is left unreacted in the vessel is discharged through the gas-outlet port.
In operation, the heater heats the crystal substrate, which is held by the holder, to a predetermined temperature. Then, feed gas (SiH.sub.4, SiH.sub.2 Cl.sub.2, SiHCl.sub.3, SiCl.sub.4, Si.sub.2 H.sub.6, or the like) are supplied into the reaction vessel through the gas-inlet port, along with carrier gas (H.sub.2 or the like).
In most cases, a device having a lamp, a high-frequency wave generator, or a electric resistor is utilized as a heater to heat the substrate held by the holder to the predetermined temperature. Whatever heating device is used, it is necessary to heat the substrate uniformly. To this end, use can be made of a substrate holder having a recess in which to hold a crystal substrate, as is disclosed in Published Unexamined Japanese Patent Application No. 61-215289 and No. 62-4315. Even if heated while held by this holder, a substrate is heated more at its peripheral part than at the center part since the peripheral part contacts the holder. Consequently, it is very difficult to form a crystal film having a uniform thickness, on the substrate.
Recently, it is increasingly demanded that a substrate be used in its entirety. In other words, it is desired that the peripheral part of a substrate should not be cut and discarded, in order to save material. Hence, there is a great demand for a technique of forming a crystal film having a uniform thickness on the substrate, and the difference in temperature between the peripheral part and center part of the substrate can no longer be ignored.
Moreover, once the substrate warps due to the difference in temperature between the upper and lower surfaces of the substrate, the gap between the substrate and the surface of the holder changes. This temperature distribution of the substrate and the change in the surface temperature distribution results in stress. The stress is great, in particularly when the substrate is made of single-crystal silicon. It causes transition of the single-crystal silicon, which is known as "slip." The slip deteriorates the characteristics of the semiconductor devices formed on the silicon substrate.
The slip is a phenomenon that crystal molecules glides along crystal lattices and are deformed when the stress, caused by the non-uniform distribution of surface temperature of the substrate heated to a high temperature, increases above the yield point of the crystal substrate. As is known in the art, the higher the temperature of the crystal substrate, the lower the yield point of the substrate, and the higher the probability of slip.
Also, the substrate must be cooled to a low temperature some time before it is placed on and removed from the holder. It would otherwise be difficult to place the substrate on the holder, and to remove it from the holder.
As has been pointed out, in the conventional vapor-phase deposition apparatus, the peripheral part of a substrate, which contacts the holder, is more heated than the center part which does not contact the holder. The non-uniform temperature distribution of the substrate inevitably makes it difficult to form a crystal film having a uniform thickness, on the substrate. Further, once the substrate warps due to the difference in temperature between the upper and lower surfaces of the substrate, the gap between the substrate and the surface of the holder changes, inevitably changing the surface temperature distribution of the substrate. The change of the surface temperature distribution results in two problems. First, it is impossible to form a crystal film having a uniform physical property such as carrier concentration. Second, the substrate has stress, which causes transition of the single-crystal silicon, such as slip, ultimately deteriorating the characteristics of the semiconductor devices formed on the silicon substrate. Moreover, the substrate must be cooled to a lower temperature some time before it is placed on and removed from the holder, in order to facilitate the placing and removal of the substrate. Needless to say, the cooling of the substrate is a bar to enhancement of throughput of the vapor-phase deposition apparatus.